Solar radio spectral irradiance Christophe Marqué Royal Observatory of Belgium 14/10/13SOLID Meeting WP21

The beginning Solar radio astronomy started during WWII Conversion of radar equipments into radiotelescopes No choice of frequencies 14/10/13SOLID Meeting WP22

The beginning Active Sun Sporadic activity linked to solar eruptive events Accelerated electrons (non thermal populations) Different spectral types 14/10/13SOLID Meeting WP23

The beginning Non active Sun Thermal emission from the corona (T~10 6 K, Pawsey,1946) Bremsstrahlung, Gyroresonance 2 components: Quiet Sun & SVC 14/10/13SOLID Meeting WP24

The beginning The excitement of the eclipse observations [at 10.7 cm] was soon followed by the sobering thoughts that solar radio emission from sunspots would be variable… A. Covington, Proc. NRAO Workshop, /10/13SOLID Meeting WP25

Interplanetary medium High corona Low corona Transition region Chromosphere Solar radio observations The Sun is observed in radio in a large spectral window: from far I.R to km wavelengths Plasma emission Gyrosynchroton Plasma emission Gyrosynchroton Gyrosynchrotron Thermal bremsstrahlung Gyrosynchrotron Thermal bremsstrahlung Gyroresonance Thermal bremsstrahlung Gyroresonance Thermal bremsstrahlung Unknown

Solar radio spectral irradiance Continuum emission: no lines Flux density: W.m -2.Hz -1 Solar Flux Unit: W.m -2.Hz -1 = 10 4 Jansky Intensity as Brightness Temperature 14/10/13SOLID Meeting WP27

Solar Flux radio Observatories 14/10/13SOLID Meeting WP MHz 1000 MHz 2000 MHz 3750 MHz 9400 MHz MHz 245 MHz 410 MHz 610 MHz 1415 MHz 2695 MHz 4995 MHz 8800 MHz MHz

Flux Measurement Full Sun Parabolic dish Horn antenna Pentincton: strict calibration procedure 3 times per day 14/10/13SOLID Meeting WP29

Flux measurement: calibration Tanaka (1973) paper Toyokawa: reference station Flux correction (0.9 for F10.7) Standard for absolute calibration Precision 1-2 % 14/10/13SOLID Meeting WP210

Flux measurement: natural sources of error 14/10/13SOLID Meeting WP211 Atmospheric absorption Rain Humidity (dew/snow) on antenna Temperature variation Ionospheric disturbances

Flux measurements: examples calibration Quiet Sun level Ground interference Quiet sun level Solar flare

Cycle /10/13SOLID Meeting WP213

Emission mechanism 14/10/13SOLID Meeting WP214 After Schmahl & Kundu 1998

Spectrum of QS &SVC QS : S~f 2 -> Thermal Bremstrahlung SVC: ~Flat spectrum Gyroresonance/Free- Free 14/10/13SOLID Meeting WP

Free-Free / Gyroresonance 14/10/13SOLID Meeting WP216

Quiet Sun: essentially Free-Free 14/10/13SOLID Meeting WP217 Zirin, 1991

SVC 14/10/13SOLID Meeting WP218 S. White

Last words Long term spectral irradiance with good stability (with proper calibration procedure) Care should be taken about the meaning of daily values No Instrument degration (apart from rust & spare parts availability) Possibility to use radio data for EUV/UV calibrations Gold mine for long term studies of coronal evolution (n, T, & B) 14/10/13SOLID Meeting WP219